"All people experience hardships and sorrow. Sometimes you may even wish you could vanish out of loneliness. Even so, people must endure that and live on."

During the attack that caused the Moon Kingdom's downfall, Prince Endymion died protecting Serenity. In the manga she then commits suicide out of grief, while in the anime Queen Metallia killed them both. Serenity's mother, the Queen, was able to seal away the evil that had created the attack, but everyone involved was killed. Before her own death, the Queen used the Silver Crystal to give her daughter (and others) another chance at life, hoping that Serenity and Endymion would be able to find happiness together. In the live-action series, it is Princess Serenity herself who destroys the Moon Kingdom when Endymion was killed during the war.

Serenity reincarnates as Usagi Tsukino in the 20th century. Usagi occasionally takes the form of Princess Serenity during the series, often at climactic moments when more strength is needed than Sailor Moon can usually access. Usagi discovers her identity as a princess in act 9 of the manga, episode 34 of the anime, and act 25 of the live-action series.

Otaku Trivia:

1) In Act 48 Dream 10, the Sailor Senshi suddenly recall a flashback of the celebration of the birth of Princess Serenity, and it shows Serenity as a baby and the Inner Senshi as children around the age of 6-9, implying that in the past, the Inner Senshi were older than Princess Serenity.

2) Even though the Crystal is far much more like the manga, Princess Serenity has yellow-blonde hair; like her original anime counterpart. However, her hair is noticeably a paler yellow-blonde than Usagi's, as opposed to the original anime, where Serenity had the exact same yellowish-blonde hair as Usagi.

3) During some of the climatic battles of the original anime, Sailor Moon became Princess Serenity herself, implying she is at her strongest and most powerful while in that form, whereas in the manga, Sailor Moon defeats the main antagonists without becoming Princess Serenity.